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Re: T1 vs. T2 [WAS: Apology: [Tier-2 reachability and multihoming]]

  • From: Dorian Kim
  • Date: Tue Mar 29 15:52:05 2005

On Tue, Mar 29, 2005 at 02:27:56PM -0600, John Dupuy wrote:
> I was looking at it from a route announcement point of view. Transit is 
> where AS A advertises full routes to AS B. Thus, AS B is getting transit 
> from A. Peering is where A & B only advertise their network and, possibly, 
> the networks that stub or purchase transit from them.
> It is my understanding that the top ISPs "trade transit". They provide full 
> routes to each other without payment, regardless of how or where the route 
> was learned from. They are willing to pass some traffic without 
> compensation because it makes for better connectivity. From an announcement 
> POV they are not peering.
> I am still curious: do any of the larger ISPs on this list want to 
> confirm/deny the previous paragraph?

ISPs formerly known as tier1s in general peer with each other, not trade transit. 
If one of the peers started sending us full routes, that would quickly result in a 
NOC to NOC chat about route leaks.

If they exchanged full routes, wouldn't that be mutual transit, not peering?

This isn't meant to imply that networks don't play kinky games with each other
at various times that can confuse outside observers, but peering is peering
and transit is transit, most of the time.


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